1. Technical Field
The present disclosure relates to a module substrate including an optical transmission mechanism for signal transmission, and a method of producing the module substrate.
2. Related Art
In accordance with speeding up of information transmission, a method in which optical communication using an optical waveguide is employed in place of an electric signal has been studied. In the case where a signal is transmitted between a Central Processing Unit (CPU) and an Integrated Circuit (IC), in a conventional method in which transmission is performed using electric wiring, for example, a wiring delay in which the propagation speed of the signal is reduced depending on the length of the wiring, electromagnetic noises which are caused by the transmitted signal, and a delay of the signal propagation speed which is caused by impedance mismatching significantly appear when the transmission speed (frequency) of the signal is very high. Consequently, there arises a problem in that the process speed of an electronic device is restricted depending on the transmission speed of the signal.
By contrast, in a method using an optical waveguide in place of an electric wiring (i.e., a method using light in communication), the problems such as a signal delay, electromagnetic noise, and impedance mismatching are not occurred. Therefore, the method can be effectively used for increasing the signal transmission speed. As a method using light in signal transmission, for example, a method has been studied in which an optical waveguide is formed in a wiring substrate on which an IC is mounted, and, in addition to electrical signal transmission through an electric wiring, optical signal transmission using the optical waveguide is enabled (for example, see JP-A-2004-86185 and JP-A-2006-39045).
In the case where a signal transmission mechanism using an electric wiring, and that using light are to be provided in a wiring substrate, a signal transmission path using light must be placed so that a signal transmission path using the electric wiring is shortened as far as possible, thereby enabling signal transmission to be performed at higher speed. A signal transmission path using light has a structure which is different in kind from that of an electric wiring. Therefore, the electric wiring and the optical waveguide must be placed while they are surely combined with each other, and also it is requested to enable the mechanisms to be produced without complicating production steps.